1. Field of the Invention
The invention relates to communications apparatuses and methods for the communications apparatuses to autonomous fast return to a preferred RAT (Radio Access Technology).
2. Description of the Related Art
The evolution of wireless communications technologies often requires that newer systems and networks be compatible with existing systems and networks. A communications specification defining the operation of new technology often provides requirements for the new system to interface with these legacy systems. For example, the 3GPP Long Term Evolution (LTE) standard requires that a wireless communications device be able to use circuit switched networks for voice calls as well as utilize the LTE network. For example, LTE allows a circuit switched fall back (CSFB) procedure, in which an LTE handset can leverage the existing infrastructure of previous 2G or 3G technologies to make or receive voice calls. In other words, the LTE handset can end an existing LTE connection with an LTE evolved Node B (eNB) and fall back to a 2G or 3G cell (e.g., Node B or base station). During the CSFB procedure, the LTE session is suspended. Upon completion of the call, the LTE handset can then re-establish a connection with the LTE network. For another example, some operators may require a wireless communications device to be able to transfer a circuit switched service from a 3G network to a 2G network due to the 3G network not being as widely distributed as the 2G network or the 3G network being configured to only provide packet switched services.
When switching between different radio access technologies (RATs) is required, for example, switching from 4G to 3G/2G or switching from 3G to 2G as the examples given above, long delay time usually occurs. A long delay time can be frustrating for the user and can degrade the overall communications performance.
Therefore, a method for autonomous fast return to the original RAT is proposed.